The present invention relates to an apparatus for inspecting the external appearance of wire bonding between a semiconductor chip and leads.
After wire bonding between a semiconductor chip and leads has been completed, it is necessary to inspect whether wires are bonded at their correct positions, in straight lines without being curved, not disconnected, etc. These external appearance inspections can be carried out by automatically processing an image obtained by a camera.
During inspection, it is necessary to illuminate the semiconductor chip, wires, and leads to be inspected. In the prior-art inspection, these objects to be inspected have been illuminated as shown in FIG. 4. In the drawing, a bed 13 of a lead frame 18 is supported by tie bars 15, and semiconductor chips 11 are mounted on this bed 13. Wires 17 are connected between electrodes 11a of the semiconductor chip 11 and leads 14 arranged near the bed 13 as shown.
These objects to be inspected are imaged by a camera 21 disposed thereover under illumination of a downward illuminating means 2 disposed in the vicinity of the camera 21 for illuminating the objects from above.
In the prior-art apparatus, however, since only a single illuminating means is provided, the illumination direction is limited to one direction, thus causing a problem in that the illumination intensity is not sufficient, for each of the items to be inspected and therefore the inspection reliability is inevitably degraded. In more detail, there are some inspection items such as the detection of the position of a reference mark 12 representative of a reference position used to determine the coordinates of the semiconductor chip 11, the detection of the position of another reference mark 16 representative of a reference position of a lead frame 18, the inspection of shapes of the leads 14, the inspection of shapes of the bonded wires 17, etc.
In each of these inspections, the optimum illumination direction differs. For instance, when the position of the reference mark 12 is required to be detected, it is preferable to illuminate the semiconductor chip 11 from above. When inspecting other items, however, this illumination direction is not preferable and therefore a satisfactory image cannot be obtained. Where a high quality image cannot be obtained by the camera 21 for inspection purposes, there exists a problem in that the inspection reliability is degraded and therefore a sufficient guarantee for the product quality cannot be achieved. In addition, where the inspection is made on the basis of a dissatisfactory image, there exists a problem in that a long image processing time is required, thus increasing the inspection cost.